Dispensers for a stack of articles typically have a frame that defines a cavity to receive the articles. A platform in the cavity supports the articles. The level of the top article in the stack is maintained by adjusting the level of the platform using a force to counter the weight of the article(s) on the platform. The counter force can be provided by springs either alone or in combination with pulleys. The counter force is varied so that the top article is at a desired height in the dispenser when the platform is at the adjusted level.. Therefore, these dispensers are self-leveling in that the dispenser is capable of maintaining the top article at the desired height when an article is added to, or removed from, the dispenser without an operator adjusting the level of the platform.
In operation, when an article is placed onto the platform or stack the extra weight temporarily overcomes the counter force and lowers the platform so the platform or top article is at the desired height. When an article is removed from the stack, the decrease in weight permits the counter force to raise the platform so that the top article is at the desired height.
Representative articles include dinnerware, trays, food containers and the like.
The dispensers are often used in the food industry, e.g., restaurants and hospitals. The dispenser can be located in a heated base to keep the articles warm or to ensure sterility of the articles. The dispenser may be heated to temperatures in excess of 300.degree. F.
FIG. 1 illustrates a prior art square dispenser 10 having a frame 12 with an upper end 14 and a lower end 16. Posts 18 define the corners of the dispenser 10. A movable spring holder 20 slidably extends around the perimeter of the frame 12. Exposed springs 22 are secured to the lower end 16 and the spring holder 20. A platform 24 is slidably received within the interior of the frame 12. Pulleys 26 are located on the posts 18 near the upper end 14. A pulley 27 is located on the platform 24. A cable 28 extends from the spring holder 20 over the pulley 26, under the pulley 27, over a second pulley 26 and back to the holder 20. A second set of the pulleys 26, pulley 27 and cable 28 are present on the side of the dispenser 10 not being viewed.
The dispenser 10 has numerous shortcomings. The springs 22 are exposed to the interior of the frame 12. Thus, the articles (not shown) or the platform 24 can become entangled in the springs 22. If the springs 22 suddenly become untangled, the articles and platform 24 can quickly and unexpectedly rise, injuring the user. The exposed springs 22 can trap dirt and debris and then transfer this to clean articles or the platform 24. The presence of the dirt and debris would require recleaning of the articles and platform 24.
The prior art dispenser 10 has a number of other structural features that can also result in entangling or that can result in binding of the dispenser 10. Problems similar to those observed when untangling the springs arise when the user attempts to unbind the dispenser 10. The dispenser 10 has only two pulleys 27 on the platform 24. The leveling of the platform. 24 depends on pulleys 27. However, the platform 24 can rotate about an axis (not shown) through the pulleys 27. If the articles are unevenly loaded on the platform 24, the platform 24 can rotate and become tilted resulting in the articles or platform 24 becoming entangled in the springs 22. Alternatively, the article or platform 24 could become bound with the exposed posts 18. Also, the spring holder 20 extends around the perimeter of the frame 12. Uneven loading of the platform 24 can result in the spring holder 20 becoming bound with the posts 18.
The arrangement of the springs 22, spring holder 20, pulleys 26 and 27 and cable 28 requires that the frame 12 be rectangular in shape. Since the articles are typically round, there is an increase in likelihood of entangling or binding due to the differences in shape.
The configuration of the cable 28 and the size of the pulleys 26,27 cause excessive forces to be applied to the bearings (not shown) of the pulleys 26,27. The bearings are prone to failure due to these forces, especially at elevated temperatures. Failure of the bearings could result in the dispenser 10 being inoperable.
The force generated by the springs 22 is not increased by the arrangement of the pulleys 26,27. More or heavier springs 22 are required because there is no force increase. The use of more springs 22 increases the likelihood of tangling, binding and dirt and debris being trapped and transferred to the article. Heavier springs 22 are more expensive.
FIG. 2 illustrates a prior art round dispenser 30. A ring 32 has partially enclosed side supports 34 extending therefrom. Openings 36 are defined in the perimeter of the dispenser 30 between the supports 34. A cavity 38 within the dispenser 30 receives a platform 40 therein. A spring holder 42 is secured to the platform 40 and extends around the circumference of the dispenser 30. Springs 44 within the support 34 are secured to the ring 32 and to the spring holder 42. The springs 44 directly act upon the platform 40. The springs 44 are separated from the cavity 38 by the side 35 of the support 34.
The supports 34 must be large enough to contain the multiple springs 44 required to support and lift the platform 40 and articles (not shown) thereon. The size of the supports 34 significantly reduces the size of the openings 36. This reduction in the size significantly reduces the amount of air that can flow therethrough which increases the time period required to heat, cool or dry the articles within the dispenser 30.
The springs 44 are stretched 1 inch for every 1 inch the platform 40 is lowered. Thus, the springs 44 can be extended to their absolute maximum length when the platform 40 is at its lowest position within the dispenser 10. Stretching the springs 44 to their absolute maximum length can result in the springs 44 taking a set (a non-recoverable deformation), especially at an elevated temperature. A spring 44 that takes a set will not contract to its original, fully contracted length but rather will only contract to a longer length. When a spring 44 loses its ability to contract to its original, fully contracted length, the force on the platform 40 can be uneven which results in entanglement or binding. The undesirability of a tangled or bound dispenser 10 is discussed above. Furthermore, when the spring 44 takes a set, the force on the platform 40 is lessened which can result in the platform 40 no longer being self-leveling which results in the top article (not shown) not being at the desired height.
The force generated by the springs 44 is applied to the platform 40 with no increase in force which requires more springs 44 than a structure wherein the force is increased. The use of more springs 44 increases the size of the supports 34 and decreases the size of the openings 36 which reduces air flow.
The cavity 38 has an overall length L1, a usable length L2 and an unusable length L3 when the platform 40 is at the bottom of the cavity 38. Thus, only a percentage of the length of the cavity 38 can be used to hold articles. The unusable length L3 is due to the springs 44 being fully contracted when the platform 42 is at the top of the cavity 38. Increasing the length of the cavity 38 requires that longer springs 44 be used which have a longer fully contracted length. The platform 42 will not be at the top of the cavity 38 because the longer springs 44 cannot be contracted any more. The thickness of the platform 42 must be increased so that it will be at the top of the cavity 38. Increasing the thickness of the platform 42 increases the unusable length L3 as the overall length L1 increases. Thus, the unusable length L3 is dependent upon the length of the fully contracted springs 44. Increasing the number of articles that can be held by increasing the overall length is impractical.
The length of the dispenser can be limited by the base which is designed to hold the dispenser therein. Therefore, it is not possible to increase the length of the dispenser to increase the number of articles that can be held therein. Furthermore, as the length of the dispenser increases, the more costly it is to obtain springs that do not take a set.
A dispenser that is self-leveling and which does not exhibit at least one of the aforementioned shortcomings is highly desirable.